Expanding agroforestry can increase nitrate retention and mitigate the global impact of a leaky nitrogen cycle in croplands

The internal soil nitrogen (N) cycle supplies N to plants and microorganisms but may induce N pollution in the environment. Understanding the variability of gross N cycling rates resulting from the global spatial heterogeneity of climatic and edaphic variables is essential for estimating the potential risk of N loss. Here we compiled 4,032 observations from 398 published N-15 pool dilution and tracing studies to analyse the interactions between soil internal potential N cycling and environmental effects. We observed that the global potential N cycle changes from a conservative cycle in forests to a less conservative one in grasslands and a leaky one in croplands. Structural equation modelling revealed that soil properties (soil pH, total N and carbon-to-N ratio) were more important than the climate factors in shaping the internal potential N cycle, but different patterns in the potential N cycle of terrestrial ecosystems across climatic zones were also determined. The high spatial variations in the global soil potential N cycle suggest that shifting cropland systems towards agroforestry systems can be a solution to improve N conservation.

Automated summary

By analyzing the interactions between soil internal potential nitrogen cycling and environmental effects, it was found that the global potential nitrogen cycle is more conservative in forests, less conservative in grasslands, and leaky in croplands. The study showed that soil properties are more important than climate factors in shaping the internal potential nitrogen cycle, but different patterns in the potential nitrogen cycle of terrestrial ecosystems across climatic zones were also determined. The high spatial variations in the global soil potential nitrogen cycle suggest that shifting cropland systems towards agroforestry systems can be a solution to improve nitrogen conservation.